Although today's media inaccurately, and irresponsibly, designate semi-automatic firearms as being "automatic" weapons, one must not lose sight of the fact that there is a significant distinction between a semi-automatic and an automatic (perhaps, more accurately, a "fully automatic") firearm.
Semi-automatic firearms do--in response to the discharge of the firearm--eject a spent cartridge casing and sequentially feed a loaded cartridge into the chamber. However, a semi-automatic firearm will not fire the cartridge so loaded until the trigger has been released and then sequentially re-depressed. That is, even if the shooter maintains the trigger depressed in the firing position after a cartridge has been fired, the successively chambered cartridge will not be discharged without the aforesaid release and re-depression of the trigger. Such a firearm may be an "auto-loading" firearm--i.e., a semi-automatic firearm--but it is not an automatic firearm.
Generally speaking, an automatic firearm, will, to the contrary, continue to fire all available rounds in the magazine so long as the trigger remains depressed. By way of an exception, it should be noted that there are automatic firearms which will selectively discharge bursts of only a predetermined number of rounds in response to depressing the trigger only one time, but they are still automatic firearms.
It must be understood that it is forbidden by the National Firearms Act to possess automatic firearms within the United States, or the District of Columbia, without special authorization, and full details covering compliance with that Act are available from the Department of the Treasury, the Bureau of Alcohol, Tobacco and Firearms, commonly designated as the B.A.T.F.
When one understands the operational distinction between automatic and semi-automatic firearms, it can be readily understood that the cyclic firing rate for a semi-automatic firearm is normally limited by the reaction time within which the shooter can squeeze the trigger to fire a round, release the trigger as the firearm recoils in response to discharge of the first round, and then re-squeeze the trigger to discharge the next successive round. Although the cyclic time will differ from shooter to shooter, even the most practiced shooter will be unable to discharge more than two or three rounds at a rate less than about one round per second.
One prior known attempt to enhance the cyclic firing rate of a seni-automatic firearm is sold under the trademark HELL-FIRE (or, more recently, HELL-STORM) and is often designated as the "Hell Fire System" or "HFS".
The HFS constitutes a spring biased paddle that engages the rear of the trigger and continually urges it forwardly. To operate the HFS, one balances the firearm by supporting it with one hand--viz., by grasping the fore-end of the stock with the hand other than the hand having the trigger finger--and then placing the trigger finger across the trigger without depressing the trigger. The trigger is depressed by pushing the fore-end of the stock, with the supporting hand, toward the target and allowing that movement to bring the trigger into contact with the trigger finger in order to depress the trigger and discharge the firearm.
The discharge recoil moves the entire weapon--including the trigger--rearwardly, and thereafter the biasing action of the paddle against the rear of the trigger moves the trigger forwardly a sufficient distance to reset the trigger so that continued forward pressure applied to the fore-end of the stock by the hand that is supporting the firearm will translate the firearm forwardly, and thereby bring the trigger into engagement against the trigger finger with a sufficient force to re-depress the trigger. The trigger finger is not to be moved.
The aforedescribed operation of the HFS is difficult to master and does not lend itself to accuracy inasmuch as the stock is never permitted to rest firmly against the shooter's shoulder--nor is the hand containing the shooter's trigger finger permitted to grasp the firearm firmly, as required to achieve even a modicum of accuracy.